The conventional Public Switched Telephone Network (PSTN) is a circuit switched network in which calls are assigned dedicated circuits during the duration of the call. Such networks are well known in the art, and service providers have developed various services which may be provided to subscribers via such a conventional circuit switched network.
Recently, data packet networks, such as local area networks (LAN) and wide area networks (WAN) have become more prevalent. These data packet networks operate in accordance with the internet protocol (IP) and such networks are referred to as IP networks. The popularity of IP networks has created an interest in providing voice and related services over IP networks.
Conventional PSTN voice services dedicate a circuit connection between a calling and called party, and as such, that connection is guaranteed a certain level of performance because it is not shared with any other network users. IP networks, on the other hand, are shared networks in which the network resources are shared between users. The notion of a connection in a data packet network is very different from the notion of a connection in a circuit network. In a circuit network, the connection is a dedicated circuit which is used only by the calling and called parties. As such, it is easy to guarantee a certain level of service via the circuit network. However, the dedication of a circuit between all calling and called parties is frequently inefficient because such dedicated circuits provide more bandwidth than is necessary. In a data network, the connection between two parties is not dedicated, and traffic between the parties is transmitted via the data packet network along with the data packets of other users. There is no dedicated path between the parties, and data packets may be transmitted between the parties via different paths, depending upon network traffic.
In the PSTN, call setup and call control services are controlled by a signaling network in accordance with the well known Signaling System No. 7 (SS7). An SS7 network exists within the PSTN network and controls call setup by conveying labeled messages via signaling channels which are separate from the voice channels. The details of an SS7 network are well known and, therefore, the details will not be described in further detail herein.
Unlike traditional PSTN calls, voice calls placed over Voice over Internet Protocol (VoIP) networks employ a variety of call control services using a variety of signaling protocols, for example, H.323-over-IP and Session Initiation Protocol (SIP)-over-IP. The H.323 standard is a comprehensive and very complex suite of protocols that provide specifications for real-time, interactive videoconferencing, data sharing and audio applications such as IP telephony. The SIP protocol is a more recent protocol that was developed specifically for IP telephony in view of popular web-based services. More efficient than H.323, SIP takes advantage of existing protocols to handle certain parts of the call control process. Due in part to these advantages over the H.323 standard, SIP has recently been adopted in VoIP networks with greater frequency. However, while SIP-based telecommunications networks are advantageous, not all networks and components support SIP—many such networks, for example, still rely on the H.323 standard which uses different protocols. In contrast to the SS7 network utilized in the conventional PSTN network, messages in VoIP networks using VoIP signaling protocols, such as the H.323 and SIP protocols are not transmitted via a dedicated signaling network, but are transmitted like any other data packets.
Developing an architecture that facilitates communication services in networks relying on such multiple existing protocols is difficult. This difficulty arises because, as discussed above, different call control/signaling protocols use different signaling mechanisms and messages that are not recognized by other protocols. For example, in some implementations, originators of calls requiring advanced features use the H.323 protocol to access a communications provider's core SIP network. Therefore, there is a need to permit SIP networks to coexist with such more traditional networks, such as IP networks operating with a different protocol, such as the H.323 protocol.